Abstract
Acetaminophen (APAP) is safe at therapeutic levels but causes hepatotoxicity via N-acetyl-p-benzoquinone imine-induced oxidative stress upon overdose. To determine the effect of human (h) pregnane X receptor (PXR) activation and CYP3A4 induction on APAP-induced hepatotoxicity, mice humanized for PXR and CYP3A4 (TgCYP3A4/hPXR) were treated with APAP and rifampicin. Human PXR activation and CYP3A4 induction enhanced APAP-induced hepatotoxicity as revealed by hepatic alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities elevated in serum, and hepatic necrosis after coadministration of rifampicin and APAP, compared with APAP administration alone. In contrast, hPXR mice, wild-type mice, and Pxr-null mice exhibited significantly lower ALT/AST levels compared with TgCYP3A4/hPXR mice after APAP administration. Toxicity was coincident with depletion of hepatic glutathione and increased production of hydrogen peroxide, suggesting increased oxidative stress upon hPXR activation. Moreover, mRNA analysis demonstrated that CYP3A4 and other PXR target genes were significantly induced by rifampicin treatment. Urinary metabolomic analysis indicated that cysteine-APAP and its metabolite S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid were the major contributors to the toxic phenotype. Quantification of plasma APAP metabolites indicated that the APAP dimer formed coincident with increased oxidative stress. In addition, serum metabolomics revealed reduction of lysophosphatidylcholine in the APAP-treated groups. These findings demonstrated that human PXR is involved in regulation of APAP-induced toxicity through CYP3A4-mediated hepatic metabolism of APAP in the presence of PXR ligands.
Footnotes
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This work was supported in part by the National Cancer Institute Intramural Research Program; and the U.S. Smokeless Tobacco Company.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.109.027565.
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ABBREVIATIONS: APAP, acetaminophen; NAPQI, N-acetyl-p-benzoquinone imine; P450, cytochrome P450; PXR, pregnane X receptor; TgCYP3A4/hPXR, double transgenic mice expressing human PXR and CYP3A4; RIF, rifampicin; MDZ, midazolam; KTZ, ketoconazole; DEB, debrisoquin; 1′-OH-MDZ, 1′-hydroxy-midazolam; Cys-APAP, cysteine-APAP; NAC-APAP, 3-N-acetyl-cysteinyl-APAP; APAP-G, APAP O-glucuronide; APAP-S, APAP sulfate; Cont, control; Rif, rifampicin treatment alone; AP mice, mice administrated APAP; APR mice, mice administered APAP and rifampicin; ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; GSH, reduced glutathione; H2O2, hydrogen peroxide; PCR, polymerase chain reaction; qPCR, quantitative polymerase chain reaction; CT, cycle threshold; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; LC, liquid chromatography; MS, mass spectrometry; UPLC, ultra-performance liquid chromatography; SAMP, S-(5-acetylamino-2-hydroxyphenyl)mercaptopyruvic acid; TOFMS, time-of-flight mass spectrometry; IS, internal standard; PCA, principal components analysis; PLS-DA, partial least-squares discriminant analysis; GS-APAP, glutathione-APAP; ROS, reactive oxygen species; LPC, lysophosphatidylcholines; AA, arachidonic acid.
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The online version of this article (available at http://dmd.aspetjournals.org) contains supplemental material. - Accepted May 21, 2009.
- Received March 16, 2009.
- U.S. Government work not protected by U.S. copyright
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